The prior art includes, as disclosed in EP-A-481,732, a sustained-release preparation comprising a drug, a polylactic acid and a glycolic acid-hydroxycarboxylic acid [HOCE(C.sub.2-8 alkyl)COOH] copolymer. The disclosed process comprises preparing a water-in-oil (W/O) emulsion consisting of an internal water phase consisting of an aqueous solution of a physiologically active peptide and an external oil phase consisting of a solution of a biodegradable polymer in an organic solvent, adding said W/O emulsion to a medium such as water and processing the resulting W/O/W emulsion into sustained-release microcapsules (in-water drying method).
However, generally a microparticle prepared by the in-water drying method does not achieve a high drug content. In that method, the encapsulation rate of the microparticle varies widely among the lots and is easily influenced by expansion of the production scale.
A spray-drying method is also known in the art. Although the microparticles produced by this method usually have an adequate encapsulation rate, the quality of the particles varies widely according to the changes of production condition. Generally, a lot of the microparticles are aggregate or adhere together in this method. Also, the dispersion ability of the particles in an aqueous dispersion solvent is reduced as compared with that of in-water drying method.
Further, in the known method for preparing a microparticle by pulverizing a solid dispersion containing a drug and a biodegradable polymer, there is a problem that a solid dispersion prepared by using an adhesive drug, especially in a large amount, is unable to be pulverized by a general pulverizing technique.